A micro-structure produced by utilizing a MEMS technology includes a micro-mirror element, for example. The micro-mirror element is incorporated in an optical apparatus, such as an optical switch or the like, to swing a mirror surface thereof for reflecting a light, to thereby change a reflection direction (course) of the light. For example, there has been proposed an electrostatic-actuated type micro-mirror element which swings a mirror surface thereof utilizing an electrostatic force.
For example, an electrostatic actuated type micro-mirror element disclosed in Japanese Laid-open Patent Publication No. 2002-328316, includes: a frame; a mirror forming portion on which a mirror surface is formed; and a torsion bar connecting the frame and the mirror forming portion, the torsion bar can be formed to be thinner than the frame and the mirror forming portion, so that multiple design specifications of torsion bar can be obtained.
In the above-mentioned conventional technology, portions corresponding to the frame, the mirror forming portion and the torsion bar on a substrate are masked to be subjected to an etching process, and thereafter, the mask of the portion corresponding to the torsion bar is removed and the etching process is further performed, so that the torsion bar is formed to be thinner than the frame and the mirror forming portion.
However, in the above-mentioned configuration, since end portions (base portions) of the torsion bar are positioned in the vicinity of inner surfaces of the frame and side faces of the mirror forming portion, namely, “walls”, there is a possibility of shape instability of the end portions of the torsion bar, in particular, variations of size in a thickness direction thereof, depending on a mask shape, an etching recipe, a state of etching device or the like. Therefore, there is a possibility that torsional rigidity of the torsion bar, a resonance frequency of the mirror forming portion being a movable body, and further, characteristics of the micro-mirror element, are varied.
Incidentally, the above-mentioned problem, namely, the possibility of variations in the characteristics of the torsion bar due to the shape instability of the end portions thereof, is not limited to the micro-mirror element according to the above-described conventional technology, but is common to the micro-structures each of which has a configuration of supporting the movable body to be capable of swinging.